If it's not defined in the code, who would define it? They would be looking at the circumstances. They'd have familiarity, whether it's a police officer deciding whether or not to release an accused on bail, or a judge deciding whether or not to release the accused. There could be training with respect to what types of factors tend to disadvantage different groups. If, traditionally, the bail system requires people to put up money in order to be released, then they would have to be sensitive to the types of groups that might be less likely to have money and, therefore, less likely to be released. Other groups would be less likely to have a fixed address, or there may be impacts that addictions could have on the individual.
One other possible benefit of not listing a particular group but just saying, “If you're part of this group, it applies”, is to get the police officers and the judges who are applying the term to think about how it impacts the individuals in the whole process. They would try to remove any kind of discriminatory thinking about people who don't fit their mould of the “good citizen”, keeping the rest in jail.